Liquid or gaseous electrically insulating fluids are used in electrical apparatuses such as transformers, capacitors, switchgear, bushings, etc., and have a multitude of functions. Insulating, dielectric, fluids typically act as an electrically insulating medium separating the high voltage and the grounded parts within the apparatus and function as a cooling medium to transfer the heat generated in the current-carrying conductors. Additionally, analysis of the fluids provides a means to monitoring the health of an electrical equipment during operation.
In addition to the above mentioned basic functions, the insulating fluid should also comply with other necessary and desired requirements. The fluid when used in electrical equipment should contribute to a high efficiency, longer operational life time, and minimal environmental impact. Further, the fluid has to be compatible with the materials used in the electrical equipment and it should not constitute a hazard for the health and safety of personnel. In practice, insulating fluids should exhibit various physical, electrical, and chemical properties. All of these properties are regulated through standards and specifications that stipulate requirements for each one. In particular the flash and fire points of the fluid should be high enough for avoiding fire during faults in the electrical apparatus in which it is used.
Traditionally, petroleum-based oils have been used as the insulating fluid in fluid-filled transformers mainly because of the advantageous properties relating to low viscosity, low pour point, high dielectric strength, easy availability and low cost. During the last couple of decades, the transformer industry has been undergoing several changes. The market demand for compact and efficient transformers with guaranteed long-term performance coupled with the problems of corrosive sulphur and oil quality issues have warranted the need for enhancement in the properties of transformer fluids. Further, strict environmental regulations towards health and safety have been steadily evolving and the increased liability risks in the case of transformer fires or outages have raised a cause for concern. Mineral oils have poor biodegradability, have relatively low fire points and therefore they are not environmentally friendly and fire-safe. Considering these aspects, ester-based dielectric fluids have been gaining lots of attention for liquid-filled transformer applications, especially for distribution class transformers.
Today, the best alternative to mineral oil is ester liquids. Esters are advantageous due to their high biodegradability and high fire/flash points (>300° C.). Some of their properties e.g. high kinematic viscosity and more importantly their high cost have restricted their extensive use in electrical applications. In view of the global push for a clean, safe and healthy environment, there is need for insulating fluid with dielectric/physical properties similar to mineral oils and biodegradability and fire-point significantly higher than mineral oils, but also which is available at a cost similar to that of mineral oil.
Regarding biodegradability, there are no specific methods to test the biodegradability of dielectric liquids. One of the commonly used methods is the OECD 301B, the so-called modified Sturm test. The test is based on the degradation of a chemical in a nutrient solution by a mixture of microorganisms obtained from the environment. The CO2 evolved when the substance is completely oxidized is used to classify whether a substance is biodegradable or bioresistant. A substance is considered readily biodegradable if 60% CO2 evolves from the mixture in 10 days of incubation which is counted from the day when 10% of CO2 evolution is attained. The test must end in 28 days. A substance is considered biodegradable if 60% CO2 evolves by the end of 28 days using the same methodology of counting days as described above. Otherwise the substance is considered bioresistant.
Isoparaffin refers to a group of branched saturated hydrocarbons, also known as alkanes.
There are processes for producing saturated hydrocarbons from unsaturated hydrocarbons, e.g. as set out in the US document below.
US 2008/146469 discloses a process for producing a saturated aliphatic hydrocarbon prepared using an alpha-olefin as a raw material, including the steps of: producing a vinylidene olefin by dimerizing the alpha-olefin in the presence of a metallocene complex catalyst; further dimerizing the vinylidene olefin in the presence of an acid catalyst; and hydrogenating the obtained dimer. Further, there is provided a lubricant composition containing the saturated aliphatic hydrocarbon compound produced by the process.
WO 2012/141784 discloses isoparaffins derived from hydrocarbon terpenes such as myrcene, ocimene and farnesene, and methods for making the same. The isoparaffins have utility as lubricant base stocks.
Terpenes are organic compounds produced by many different plants. Terpenes are derived biosynthetically from units of isoprene, where a terpene is a molecule formed by a plurality of linked isoprene units. Traditionally, all natural compounds built up from isoprene subunits and for the most part originating from plants are denoted as terpenes. Sometimes, terpenes are also referred as isoprenoids. In nature terpenes occur predominantly as hydrocarbons, alcohols and their glycosides, ethers, aldehydes, ketones, carboxylic acids etc.
WO 2012/116783 discloses a yeast cell and the use of said cell for the production of one or more terpene(s). Further, the document relates to methods of generating said cell and the production of one or more terpene(s) and a pharmaceutical or cosmetical composition, a lubricant or transformer oil comprising said terpene(s).